Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, proper power consumption of a user equipment (UE), and the like are defined as requirements.
A cell selection procedure is a procedure for selecting a cell in which a service is provided to the UE. In general, the UE selects a cell having a strongest signal characteristic value by performing a signal measurement procedure with a base station (BS) in all searchable frequency bands. When the UE moves far from a serving cell currently providing a service to the UE, the UE reselects a desired cell capable of receiving a signal with a better characteristic. This is called a cell reselection procedure. The cell reselection procedure is to select a more desired cell according to a criterion for signal measurement and for cell reselection in an idle state. The UE may request a network to provide a service or may wait in the idle state to receive the service from the network. When in the idle state, the UE repeats the cell reselection procedure in which a cell having a better signal characteristic is reselected by measuring signals of the serving cell and its neighbor cells.
If the cell reselection procedure is performed using only signal measurement of the UE, a system load (e.g., a camp load or a traffic load) may be generated when a large number of UEs are located in one cell. In this case, the BS cannot properly distribute the system load. The cell reselection procedure is important to provide a better quality of service to a UE having mobility.
Accordingly, there is a need for a method of effectively performing a cell reselection procedure of a UE.